Tape drive apparatus and method

ABSTRACT

Disclosed is a method of storing data on a tape medium in at least one data recording session employing a tape drive apparatus operable to record the data in accordance with a format specifying an unused area of the tape medium. The method comprises formatting the tape medium according to the format, and recording a tape medium identifier in the specified unused area of the tape medium.

BACKGROUND AND RELATED ART

For several decades, magnetic tape media and corresponding data storagedevices known as tape drives have been used for storing digital data innon-volatile form, most commonly with the application of providingsecondary or backup storage and retrieval. Initially the magnetic tapeswere wound about large reels in similar manner as film for filmprojectors. In more recent years the magnetic tape has typically beenhoused in a cartridge or cassette, extending internally in the cartridgefrom a supply reel to a take-up reel. To allow interoperability betweendifferent tape media and tape drives, including those of differentvendors, the mechanical dimensions and magnetic properties of the tapemedia, as well as the exact method according to which data is to berecorded on the tape media are typically governed by agreed industrystandards.

With corporations shifting from single tape drives attached to singlehost computers to deploying large numbers of tape drives organised intape libraries, the ability to use tape media interchangeably with alarge number of tape drives has grown in importance. Adherence of tapemedia and tape drives used in a corporation to a common format, or to aset of compatible formats is therefore of great value. In anotherconsequence, in order to early diagnose technical problems with aparticular tape medium or tape drive it becomes increasingly importantto be able to uniquely identify and track the tape usage history of eachtape medium.

One known format of magnetic tape media for providing storage andretrieval of digital data is the Digital Data Storage (DDS) format,which has evolved from Digital Audio Tape (DAT) technology and developedthrough a number of versions. Each new version provided improvementsover the preceding version, among those being one or more of enlargedcapacity of the tape medium, higher speed of data recording andretrieval, improved reliability, and additional functionality for tapemedium management.

The 6^(th) version of the DDS format, which is known as DAT 160,provides the capability of the tape drive to uniquely identify a tapemedium by recording a unique cartridge serial number on the tape medium.A further improvement introduced by the DAT 160 version is thecapability to store an extended log of tape usage information on thetape medium, the extended log including twelve log sections in whichtape usage information is recorded relating respectively to the lasttwelve data recording sessions. Tape usage information recorded in eachlog section includes usage and error statistics as well as anidentification of the tape drive on which the tape medium was loadedduring the respective session. Tape media complying with the DAT 160version of the DDS format cannot be read or written to using tape drivesproduced according to an earlier version of the DDS format.

Among the versions of the DDS format in widespread use are the 3^(rd),4^(th), and 5^(th) version, known respectively as DDS-3, DDS-4, andDAT-72. These versions do not provide within their respective formatspecifications for the storage of a tape medium identifier that wouldallow uniquely identifying a tape medium.

The TapeWare backup application (http://www.yosemitetech.com/products/tapeware/) embeds a tape medium identifier within user datawritten to a tape medium. This identifier is lost when a differentapplication is used to overwrite the user data on the tape medium.

SUMMARY OF THE INVENTION

According to the present invention, there is now provided a method ofstoring data on a tape medium in at least one data recording sessionemploying a tape drive apparatus operable to record the data inaccordance with a format that specifies an unused area of the tapemedium. The method comprises formatting the tape medium according to theformat, and recording a tape medium identifier in the specified unusedarea of the tape medium.

The invention is advantageous because it enables to uniquely identifythe tape medium in a backward compatible way. Because the formataccording to which the tape medium is formatted specifies an unusedarea, the tape medium on which the tape medium identifier is recordedduring a data recording session in the tape drive apparatus can beloaded for further data recording sessions not only on the tape driveapparatus itself but also on a legacy tape drive apparatus that iscompliant with the format and does not alter the unused area. Recordingsessions employing the legacy tape drive apparatus do not affect theunused area of the tape medium, where the tape medium identifier isstored. Therefore, the tape medium identifier will not be overwritten,erased, or altered during recording sessions employing the legacy tapedrive apparatus. When after one or more recording sessions employing thelegacy tape drive apparatus the tape medium is again loaded on the tapedrive apparatus, the unchanged tape medium identifier allows the tapedrive apparatus to uniquely identify the tape medium.

For example, when the legacy tape drive apparatus is one of an installedbase of legacy tape drive apparatuses used by an enterprise, the legacytape drive apparatuses being operable to record data on tape mediaaccording to a common format, the enterprise can use the same type oftape media interchangeably in all of the legacy tape drive apparatuses.The present invention enables the enterprise to supplement the installedbase of legacy tape drive apparatuses with enhanced tape driveapparatuses that are capable of uniquely identifying tape media, and usethe same type of tape media interchangeably in both the legacy tapedrive apparatuses and the enhanced tape drive apparatuses. In this waythe enterprise benefits from the continued interchangeability of thetape media among the tape drive apparatuses without the high cost ofreplacing all legacy tape apparatuses with enhanced tape driveapparatuses.

In accordance with an embodiment, the method further comprisesdetermining whether the unused area of the tape medium comprises apreviously recorded tape medium identifier, and reading the previouslyrecorded tape medium identifier from the unused area for re-use of thesame tape medium identifier for the recording of the tape mediumidentifier. This embodiment is particularly advantageous because itenables the tape medium to remain uniquely identifiable even after beingsubjected to re-formatting in the tape drive apparatus.

In accordance with an embodiment, the method further comprisesdetermining whether the tape medium has previously been formatted. Therecording of the tape medium identifier is then performed only when theunused area of the tape medium comprises a previously recorded tapeidentifier or the tape medium has not previously been formatted. Therecording of the tape medium identifier is not performed for tape mediathat have initially been formatted in the legacy tape drive apparatus,which does not record a tape drive identifier in the unused areaaccording to the present invention, or that have been re-formatted inanother tape drive apparatus compatible with the format that erases thetape medium identifier from the unused area during formatting. Thisembodiment is particularly advantageous because it enables to track theentire history of past use of a tape medium using the tape mediumidentifier, by relying on the tape medium having been identifiable bythe same tape medium identifier throughout its entire history of pastuse.

In accordance with an embodiment, the format further specifies the tapemedium to comprise mandatory content in a specified location on the tapemedium, for example tape management information or separator marks thatseparate different areas of the formatted tape medium. The determiningwhether the tape medium has previously been formatted comprises readingdata from the specified location of the tape medium, detecting from thedata whether the tape medium comprises the mandatory content in thespecified location, and determining that the tape medium has previouslybeen formatted when the tape medium comprises the mandatory content inthe specified location.

In accordance with an embodiment, the determining whether the tapemedium has previously been formatted further comprises writing firsttest data to a test location of the tape medium, and reading second testdata from the test location of the tape medium. Comparing the secondtest data with the first test data, an error rate is calculated based onthe comparison. The tape medium is determined to not have previouslybeen formatted when the tape medium does not comprise the mandatorycontent in the specified location and the error rate does not exceed apredefined threshold. This embodiment is particularly advantageousbecause it enables to prevent erroneously finding the tape medium to beunformatted when clogged tape heads or other causes interfere withreading any data from the tape medium.

In accordance with an embodiment, the format further specifies a countof data recording sessions in a tape drive apparatus to be stored in asystem area of the tape medium. The method further comprises reading thecount of recording sessions from the system area of the tape medium,updating the count of recording sessions, and recording an extended logof tape usage information in the unused area of the tape medium, theextended log comprising the updated count of recording sessions. Beingrecorded in the unused area, the extended log is not altered duringrecording sessions in the legacy tape drive apparatus and thus in thiscase will not reflect the last recording session of the tape medium. Incontrast, the legacy tape drive apparatus as every tape drive apparatusthat is in compliance with the specifications of the format does updatethe count of recording sessions in the system area.

This embodiment is particularly advantageous because it enables to storeon the tape medium tape usage information that relates to the presentrecording session and is not limited by the specifications of theformat. Because the extended log comprises a count of recording sessionsreflecting the recording session during which the extended log wasrecorded, the embodiment enables to compare the count of recordingsessions from the extended log to the count of recording sessions fromthe system area to determine whether the extended log refers to the lastrecording session.

According to an embodiment, the extended log comprises a plurality oflog sections in which tape usage information is recorded relatingrespectively to corresponding ones of the at least one data recordingsessions, the log sections together constituting a cumulative record oftape usage, each log section in respect of a recording sessioncomprising the count of recording sessions. This embodiment isparticularly advantageous because it enables to provide a cumulativerecord of tape usage on a tape medium formatted according to a formatthat does not specify such a cumulative record.

In another aspect the present invention relates to a backward compatiblestorage apparatus for storing data on a sequential storage medium. Theapparatus comprises means for transferring data between the sequentialstorage medium and the backward compatible storage apparatus in at leastone data recording session, and means for formatting the sequentialstorage medium according to a legacy format. The legacy format specifiesan unused area of the sequential storage medium that is unaffected bydata recording sessions employing the legacy storage apparatus. Thebackward compatible storage apparatus further comprises means forrecording an identifier of the sequential storage medium in the unusedarea of the sequential storage medium.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention will be described ingreater detail by way of example only making reference to the drawingsin which:

FIG. 1 is a block diagram of a tape drive apparatus of an embodiment,and a legacy tape drive apparatus to which it is backward compatible,

FIG. 2 is a schematic depiction of a layout of a tape medium, on whichdata have been stored according to a method embodying the invention,

FIG. 3 is a flowchart of a method embodying the invention,

FIG. 4 is a flowchart of a determining step of an embodiment, and

FIG. 5 is a diagram depicting the recording of an extended log of tapeusage according to an embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a first tape drive apparatus 102embodying the present invention, and a second tape drive apparatus 104to which the first tape drive apparatus 102 is backward compatible. Thefirst tape drive apparatus 102 comprises a data transfer unit 106,adapted to load a tape medium 100 and capable of transferring databetween the loaded tape medium 100 and the first tape drive apparatus102. The second tape drive apparatus 104 analogously comprises a datatransfer unit 106′ adapted to load the same tape medium 104 and capableof transferring data between the tape medium 104 and the second tapedrive apparatus.

The first 102 and second 104 tape drive apparatuses comprise respectivedata processing units 134, 134′ for controlling the reading and writingof data on the tape medium 100. The data processing unit 134 of thefirst tape drive apparatus 102 is connected via an interface 135 to ahost computer 136 comprising a processor 138 capable of executing abackup application 140 for sending commands and data to be stored on thetape medium 100 to the data processing unit 134. Analogously, the dataprocessing unit 134′ of the second tape drive apparatus 104 is connectedvia an interface 135′ to a host 136′ comprising a processor 138′ capableof executing a backup application 140′ for sending commands and data tobe stored on the tape medium 100 to the data processing unit 134′ whenthe tape medium 100 is loaded on the second tape drive apparatus.

The data processing unit 134 of the first tape drive apparatus comprisesa formatting module 108 operable to control the data transfer unit 106to format the tape medium according to a format that is compatible withan analogous formatting module 108′ of the second tape drive apparatus104. In operation, after having been formatted either in the first tapedrive apparatus 102 under the control of formatting module 108, or inthe second tape drive apparatus 104 under the control of formattingmodule 108′, tape medium 100 can be loaded interchangeably on either thefirst 102 or the second 104 tape drive apparatus for data recordingsessions, in which data stored in preceding recording sessions isoverwritten or appended to.

In data recording sessions employing the second tape drive apparatus104, an unused area of the tape medium that is specified by the formatis excluded from being written to and therefore remains unaffected.Optionally, the unused area also remains unaffected when the tape medium100 is formatted in the second tape drive apparatus 104 under thecontrol of formatting module 108′.

The data processing unit 134 of the first tape drive apparatus 102comprises a recording module 110 for recording a tape medium identifierin the unused area of the tape medium 100. Optionally, the recordingmodule 110 is controlled by a determiner 112 operable to determinewhether the tape medium has previously been formatted, and whether apreviously recorded tape medium identifier is present in the unused areaof the tape medium 100. The determiner 112 relies on a first readingmodule 114 for controlling the data transfer unit 106 to read apreviously recorded tape medium identifier from the unused area of thetape medium 100. A second reading module 116 and a detector 118 enablethe determiner to determine whether the tape medium 100 has previouslybeen formatted. A writing module 120, a third reading module 122, acomparer 124, and a calculator 126 in conjunction enable the determiner112 to verify a finding that the tape medium 100 is unformatted byperforming an error rate test for testing the reliable operation of thedata transfer unit 106.

Optionally, the data processing unit 134 of the first tape driveapparatus comprises a fourth reading module 128 for reading from thetape medium 100 a count of the data recording sessions that the tapemedium 100 has so far been subjected to, the count of data recordingsessions being recorded in the system area of the tape medium 100 inaccordance with the specifications of the format. Both the first 102 andthe second 104 tape drive apparatuses comprise respective countingmodules 130, 130′ for updating the count of data recording sessionsduring a data recording session. The data processing unit 134 of thefirst tape drive apparatus optionally comprises a logger 132 forcontrolling the data transfer unit 106 to record an extended log of tapeusage information in the unused area of the tape medium 100.

FIG. 2 schematically depicts a layout of the tape medium 100 on whichdata have been stored according to a method embodying the invention. Toenable the tape medium 100 to be used for recording data in recordingsessions employing the second tape drive apparatus, the layout followsthe format specifications. As specified by the format, the layout isdivided into adjacent areas 200, 210, 214, comprising a data area 214for recording user data, a system area 210 for recording information formanaging the tape medium, in particular a count of data recordingsessions 208, and an unused area 200. The use of the unused area 200 isnot specified by the format. The unused area 200 remains unaffected byrecording sessions in the second tape drive apparatus, and optionallyalso by using the second tape drive apparatus to format the tape medium100.

While both first and second tape drive apparatuses record data in thedata 214 and system 210 areas in accordance with the specifications ofthe format, the first tape drive apparatus additionally uses the unusedarea 200 to record a tape medium identifier 202 and an extended log 212of tape usage information. Optionally, a test location 206 for writingand reading test data as part of an error rate test is also located inthe unused area. In this way it is assured that user data from the userarea and information for managing the tape medium from the system arearemain unaffected by an error rate test performed in the test location.Optionally, the test location 206 furthermore does not overlap withlocations in which the first tape drive apparatus records the tapemedium identifier 202 and the extended log 212.

When tape medium 100 is formatted in either the first or second tapedrive apparatus, mandatory content 203 specified by the format iswritten to a specified location 204 of the tape medium, optionallylocated within the system area 210. Optionally, the format specifies thelocation 204 involving a range of distances measured from the beginningof the tape medium 100, between which the mandatory content is specifiedto start. Optionally, the format further specifies the mandatory content204, for example by specifying frame numbers of data frames constitutingthe mandatory content, in such a way that compliance of the mandatorycontent with the format specifications is verifiable. In this way, thepresence of the mandatory data 204 in the specified location and itscompliance with the format specification provides a criterion enablingthe first tape drive apparatus to determine whether the tape medium 100has previously been formatted.

In accordance with the format specifications, the layout of tape medium100 can comprise further areas such as an end-of-data area following theend of the data area 214, or additional position tolerance bandsinterspersed between areas. The tape medium 100 can furthermore beformatted as a partitioned tape, in which data can be recorded in onepartition independently of data recorded in another partition of thetape medium 100, each partition comprising a separate data areacorresponding to data area 214.

FIG. 3 shows a flowchart of a method of an embodiment of the invention.In decision step 308 the tape medium is examined to determine whetherthe medium is blank or has been previously formatted. If the tape mediumis found to not have been formatted before, a new tape medium identifieris generated in step 310 to be assigned to the tape medium. Optionally,the tape medium identifier is generated in such a way that it is uniqueto the tape medium, avoiding assigning the same identifier to two ormore tape media. One way of achieving the tape medium identifier to beunique involves using a counter that changes its counter value each timethe tape drive apparatus performs a formatting operation, and combiningthe counter value with a tape drive identifier that uniquely identifiesthe tape drive apparatus. In step 302, the first tape drive apparatusrecords the tape drive identifier in the unused area of the tape medium,followed in step 300 by formatting the tape medium according to theformat, preserving the tape medium identifier recorded in the unusedarea.

If in decision step 308 it is found that the tape medium has beenpreviously formatted, in a further decision step 304 it is determinedwhether the unused area of the tape medium comprises a tape mediumidentifier. Optionally the unused area of the tape medium is unaffectedby both formatting and data recording sessions in the second tape driveapparatus, so that the unused area will be found to not comprise anydata, and a in particular comprise no tape medium identifier if the tapemedium has been used for formatting and data recording sessions in thesecond tape drive apparatus only. However, since the format does notspecify the use of the unused area, the tape medium can comprisearbitrary data frames recorded in the unused area, for example stemmingfrom recording sessions in a further tape drive apparatus that iscompliant with the format and uses the unused area for proprietarypurposes. Optionally the likelihood of misinterpreting an arbitrary dataframe recorded in the unused area as the tape medium identifier issignificantly reduced by adding a verifiable redundancy check to thetape medium identifier.

If in decision step 304 it is found that the unused area of the tapemedium comprises a tape medium identifier, in step 306 the tape mediumidentifier is read from the unused area. Optionally, step 306 isintegrated with decision step 304, in such a way that a function iscalled to read the tape medium identifier from the unused area, wherethe function either returns an indication of success together with thetape medium identifier, or an indication that the function failed toread a tape medium identifier. In step 302, the tape medium identifieris then re-recorded in the unused area, followed by formatting of thetape medium according to the format in step 300.

If in decision step 304 it is found that the unused area of the tapemedium does not comprise a tape medium identifier, the method proceedsto step 300, formatting the tape medium according to the legacy format.In this way, the method enables to rely on that any tape medium bearinga tape medium identifier in the unused area has been identifiable by thesame tape medium identifier throughout its entire history of past use.

Alternatively, the method can be modified to proceed to step 310 fromdecision step 304 if it is found that the unused area of the tape mediumdoes not comprise a tape medium identifier, generating in step 310 a newtape medium identifier for the tape medium. In this way, the methodenables to track the future use also for tape media that have not beenidentifiable by a tape medium identifier during a part of its past usehistory.

FIG. 4 shows a flowchart depicting in detail how a method of anembodiment of the invention determines whether the tape medium haspreviously been formatted. In step 410, data are read from a location ofthe tape medium that is specified by the format to comprise mandatorycontent. In step 412, the data read from the location is examined todetect whether it comprises the mandatory content. Optionally, steps 410and 412 are integrated, in such a way that a function is called to readthe mandatory content from the specified location, the functionreturning an indication of either success or failure. If the mandatorycontent is read successfully from the specified location, decision step414 arrives at the conclusion that the tape medium is formatted.

Failure to detect the mandatory content in step 412 can be caused by thetape medium being unformatted, or by improper functioning of the firsttape drive apparatus, for example by clogged tape heads preventing datafrom being read from the tape medium. In order to verify that the tapemedium is unformatted, a test is performed in steps 416-422 to confirmthat the first tape drive apparatus is functional for reading data fromthe tape medium.

In step 416, first test data are written to a test location of the tapemedium, optionally within the unused area. In step 418, second test dataare read from the same test location. In step 420, the first and secondtest data are compared, optionally in a bit-by-bit fashion. In step 422,an error rate is calculated, optionally by dividing the number of bitsfound to differ between the first and second test data by the overallnumber of bits written to the tape medium in step 416. If the calculatederror rate remains below a predefined threshold, decision step 424arrives at the conclusion that the first tape drive apparatus isfunctional for reading data from the tape medium and therefore the tapemedium has been verified to be unformatted.

If the error rate exceeds the predefined threshold, decision step 424arrives at the conclusion that the first tape drive apparatus is notfunctioning correctly. Optionally, the first tape drive apparatusindicates a trouble condition 426, for example by flashing an indicatorlight.

FIG. 5 is a diagram depicting the recording of an extended log 212 oftape usage information in the unused area 200 of the tape medium 100according to an embodiment. The same tape medium 100 is shown in fourstages, demonstrating the effect of subsequently subjecting the tapemedium 100 to a data recording session 506 in the first tape driveapparatus, a data recording session 508 in the second tape driveapparatus, and a further data recording session 506′ in the first tapedrive apparatus.

In each stage the system area 210 of tape medium 100 is shown tocomprise the count 208 of recording sessions. The contents of the systemarea 210, including the count 208 of recording sessions, are specifiedby the format, and in accordance with the format specifications updatedby both the first and second tape drive apparatuses. Optionally, thecount 208 of recording sessions is set to zero upon the first formattingof the tape medium 100, and during each recording session in either thefirst or second tape apparatus incremented by one. Optionally, duringre-formatting of the tape medium 100 in either the first or second tapedrive apparatuses, the count 208 of recording sessions is read from thetape medium and re-used for the re-formatting operation, thus preservingthe value of the count 208.

The tape medium 100 is shown in the first of the four depicted stages tocomprise a value “6” for the count of recording sessions, signifyingthat the tape medium 100 at this stage has been subjected to six datarecording sessions since it was first formatted. During data recordingsession 506 the first tape drive apparatus in reading operation 500reads the value “6” of count 208 into a volatile memory, in updatingoperation 502 increments it by one, and in writing operation 505 writesthe resulting value of “7” back to the system area 210 of the tapemedium 100.

The tape medium 100 is now ejected from the first tape drive apparatusand loaded on the second tape drive apparatus for recording session 508.The second tape drive apparatus in reading operation 500′ reads thevalue “7” of count 208 into a volatile memory, in updating operation502′ increments it by one, and in writing operation 505′ writes theresulting value of “8” back to the system area 210 of the tape medium100.

The tape medium 100 is in turn ejected from the second tape driveapparatus and loaded on the first tape drive apparatus for a furtherrecording session 506′, which results in an updated value “9” of thecount 208 of recording sessions being written to the system area 210 ofthe tape medium 100. In the way shown, the first tape drive apparatusupdates the count 208 of recording sessions analogously to the secondtape drive apparatus, observing the specifications of the format.

For each stage, the unused area 200 of the tape medium 100 is shown tocomprise the extended log 212 of tape usage information. Optionally, theextended log 212 comprises a plurality of log sections 510. Each of thelog sections 510 contains information relating to a corresponding one ofthe data recording sessions that the tape medium 100 has so far beensubjected to. In particular, each of the log sections 510 is shown tocomprise the value that the count 208 of recording sessions was updatedto during the corresponding recording session. In the first stage of thetape medium, the log sections 510 of the extended log 212 are shown asrespectively relating to the 6^(th), 5^(th), 4^(th), 3^(rd), and 2^(nd)data recording session that the tape medium 100 was subjected to sinceformatting, thus constituting a cumulative record of tape usage coveringthe previous five recording sessions.

During data recording session 506, which according to the count 208 ofrecording sessions amounts to the 7^(th) data recording session that thetape medium 100 was subjected to since formatting, the first tape driveapparatus in copying operation 510 copies the log sections 510respectively relating to the 6^(th), 5^(th), 4^(th), and 3^(rd)recording session to the respective positions previously occupied by thelog sections 510 respectively relating to the 5^(th), 4^(th), 3^(rd),and 2^(nd) recording sessions. Then, in recording operation 504 a logsection relating to the recording session 506 and comprising the updatedvalue “7” of the count 208 is written as part of the extended log 212,overwriting the position previously occupied by the log section relatingto the 6^(th) recording session.

During data recording session 508 in the second tape drive apparatus,the extended log 212 in the unused area 200 is not updated. Because thesecond tape drive apparatus updates the count 208 of recording sessions,a mismatch arises between the count 208 of recording sessions and thevalue of the count in the log section 510 of the extended log 212 thatrelates to the last recording session in the first tape drive apparatus.

During the following data recording session 506′ in the first apparatusthe same copying 512 and recording 504 operations are carried out asdescribed for the data recording session 506. There no longer is amismatch between the count 208 of recording sessions and the value ofthe count in the log section 510 of the extended log 212 that relates tothe last recording session in the first tape drive apparatus. However,because data recording session 508 employed the second tape driveapparatus, there is no section 510 relating to it in the extended log212.

Optionally, the extended log 212 is used by the first tape driveapparatus, or by an external backup or utility application for analysingthe history of past use of the tape medium. Because of thecorrespondence between the count 208 of recording sessions and thevalues of the count 208 stored in each log section 510 of the extendedlog 212, the analysing tape drive apparatus or application is enabled toidentify to which of the sequence of past recording sessions each of thelog sections 510 relates.

LIST OF REFERENCE NUMERALS

-   100 Tape medium-   102 First tape drive apparatus-   104 Second tape drive apparatus-   106, 106′ Data transfer unit-   108, 108′ Formatting module-   110 Recording module-   112 Determiner-   114 First reading module-   116 Second reading module-   118 Detector-   120 Writing module-   122 Third reading module-   124 Comparer-   126 Calculator-   128 Fourth reading module-   130, 130′ Counting module-   132 Logger-   134 Data processing unit-   135, 135′ Interface-   136, 136′ Host computer-   138, 138′ Processor-   140, 140′ Backup application-   200 Unused area-   202 Tape medium identifier-   203 Mandatory content-   204 Specified location on the tape medium-   206 Test location-   208 Count of data recording sessions-   210 System area-   212 Extended log of tape usage information-   214 Data area-   300 Formatting of tape medium-   302 Recording of tape medium identifier-   304 Determining of existence of previously recorded tape identifier-   306 Reading of previously recorded tape identifier-   308 Determining whether tape medium has previously been formatted-   310 Generating of tape medium identifier-   410 Reading from specified location-   412 Detecting of presence of mandatory content-   414 Determining that tape medium has previously been formatted-   416 Writing of first test data-   418 Reading of second test data-   420 Comparing of first and second test data-   422 Calculating of an error rate-   424 Determining that tape medium has not previously been formatted-   426 Trouble condition-   500 Reading of count of recording sessions-   502, 502′ Updating of count of recording sessions-   504 Recording of extended log-   505, 505′ Writing of count of recording sessions-   506, 506′ Data recording session in first tape drive apparatus-   508 Data recording session if second tape drive apparatus-   510 Log sections of extended log-   512 Copying of log sections of extended log

1. A method of storing data on a tape medium in at least one datarecording session employing a tape drive apparatus operable to recordthe data in accordance with a format specifying an unused area of thetape medium, the method comprising: formatting the tape medium accordingto the format, and recording a tape medium identifier in the specifiedunused area of the tape medium.
 2. The method of claim 1, furthercomprising: determining whether the unused area of the tape mediumcomprises a previously recorded tape medium identifier, and reading thepreviously recorded tape medium identifier from the unused area forre-use of the same tape medium identifier for the recording of the tapemedium identifier.
 3. The method of claim 2, further comprising:determining whether the tape medium has previously been formatted,wherein the recording of the tape medium identifier is performed onlywhen the unused area of the tape medium comprises a previously recordedtape identifier or the tape medium has not previously been formatted. 4.The method of claim 3, the format further specifying the tape medium tocomprise mandatory content in a specified location on the tape medium,the determining whether the tape medium has previously been formattedcomprising: reading data from the specified location of the tape medium,detecting from the data whether the tape medium comprises the mandatorycontent in the specified location, and determining that the tape mediumhas previously been formatted when the tape medium comprises themandatory content in the specified location.
 5. The method of claim 4,the determining whether the tape medium has previously been formattedfurther comprising: writing first test data to a test location of thetape medium, reading second test data from the test location of the tapemedium, comparing the second test data with the first test data,calculating an error rate based on the comparison, and determining thatthe tape medium has not previously been formatted when the tape mediumdoes not comprise the mandatory content in the specified location andthe error rate does not exceed a predefined threshold.
 6. The method ofclaim 5, the test location being within the unused area of the tapemedium.
 7. The method of claim 1, the format further specifying a countof data recording sessions in a tape drive apparatus to be stored in asystem area of the tape medium, the method further comprising: readingthe count of recording sessions from the system area of the tape medium,updating the count of recording sessions, and recording an extended logof tape usage information in the unused area of the tape medium, theextended log comprising the updated count of recording sessions.
 8. Themethod of claim 7, wherein the recording of the extended log isperformed only when the unused area comprises the tape mediumidentifier.
 9. The method of claim 7, wherein the extended log comprisesa plurality of log sections in which tape usage information is recordedrelating respectively to corresponding ones of the at least one datarecording sessions, the log sections together constituting a cumulativerecord of tape usage, each log section in respect of a recording sessioncomprising the count of recording sessions.
 10. The method of any one ofclaim 1, wherein the format is selected from the group consisting of:DDS-3, DDS-4, and DAT 72, the unused area being a device area specifiedby the respective format selected.
 11. A computer program product forcontrolling a tape drive apparatus, the computer program productcomprising instructions for performing a method in accordance withclaim
 1. 12. A tape drive apparatus comprising: a data transfer unit fortransferring data between a tape medium and the tape drive apparatus inat least one data recording session, a formatting module operable tocontrol the data transfer unit to format the tape medium according to aformat specifying an unused area of the tape medium, and a recordingmodule operable to control the data transfer unit to record a tapemedium identifier in the specified unused area of the tape medium. 13.The tape drive apparatus of claim 12, further comprising: a determinerfor determining whether the unused area of the tape medium comprises apreviously recorded tape medium identifier, and a first reading moduleoperable to control the data transfer unit to read the previouslyrecorded tape medium identifier from the unused area, the recordingmodule being operable to re-use the same tape medium identifier for thecontrolling of the data transfer unit to record the tape mediumidentifier when the determiner has determined that the unused area ofthe tape medium comprises the previously recorded tape mediumidentifier.
 14. The tape drive apparatus of claim 13, the determineradapted to further determine whether the tape medium has previously beenformatted, the recording module being adapted to perform the recordingof the tape medium identifier only when the unused area of the tapemedium comprises a previously recorded tape identifier or the tapemedium has not previously been formatted.
 15. The tape drive apparatusof claim 14, the format further specifying the tape medium to comprisemandatory content in a specified location on the tape medium, the tapedrive apparatus further comprising: a second reading module operable tocontrol the data transfer unit to read data from the specified locationof the tape medium, and a detector for detecting from the data whetherthe tape medium comprises the mandatory content in the specifiedlocation, the determiner adapted to determine that the tape medium haspreviously been formatted when the tape medium comprises the mandatorycontent in the specified location.
 16. The tape drive apparatus of claim15, further comprising: a writing module operable to control the datatransfer unit to write first test data to a test location of the tapemedium, and a third reading module operable to control the data transferunit to read second test data from the test location of the tape medium,a comparer for comparing the second test data with the first test data,and a calculator for calculating an error rate based on the comparison,the determiner adapted to determine that the tape medium has notpreviously been formatted when the tape medium does not comprise themandatory content in the specified location and the error rate does notexceed a predefined threshold.
 17. The tape drive apparatus of claim 12,the format further specifying a count of data recording sessions of thetape medium to be stored in a system area of the tape medium, the firsttape apparatus further comprising: a fourth reading module operable tocontrol the data transfer unit to read the count of recording sessionsfrom the system area of the tape medium, a counting module for updatingthe count of recording sessions, and a logger operable to control thedata transfer unit to record an extended log of tape usage informationin the unused area of the tape medium, the extended log comprising theupdated count of recording sessions.
 18. The tape drive apparatus ofclaim 17, the logger being adapted to control the data transfer unit torecord the extended log only when the unused area comprises the tapemedium identifier.
 19. The tape drive apparatus of claim 17, wherein theextended log comprises a plurality of log sections in which tape usageinformation is recorded relating respectively to corresponding ones ofthe at least one data recording sessions, the log sections togetherconstituting a cumulative record of tape usage, each log section inrespect of a recording session comprising the count of recordingsessions.
 20. The tape drive apparatus of claim 12, the format beingselected from the group consisting of: DDS-3, DDS-4, and DAT 72, theunused area being a device area specified by the respective formatselected.
 21. A backward compatible storage apparatus for storing dataon a sequential storage medium, the apparatus comprising: means fortransferring data between the sequential storage medium and the backwardcompatible storage apparatus in at least one data recording session,means for formatting the sequential storage medium according to a legacyformat specifying an unused area of the sequential storage medium, andmeans for recording an identifier of the sequential storage medium inthe specified unused area of the sequential storage medium.
 22. Thebackward-compatible storage apparatus of claim 21, the legacy formatfurther specifying a count of data recording sessions of the sequentialstorage medium to be stored in a system area of the sequential storagemedium, the backward-compatible storage apparatus further comprising:means for reading the count of recording sessions from the system areaof the tape medium, means for updating the count of recording sessions,and means for recording an extended log of tape usage information in theunused area of the tape medium, the extended log comprising the alteredcount of recording sessions.